Returns the url of an iPaper, given its ID.
Sample Response (iPaper Found)
<?xml version="1.0" encoding="utf-8"?>
<result>
<code><![CDATA[SUCCESS]]></code>
<message><![CDATA[Paper found.]]></message>
<data>
<paper url="/demos/21/" />
</data>
</result>
Sample Response (iPaper Not Found)
<?xml version="1.0" encoding="utf-8"?>
<result>
<code><![CDATA[PAPER_DOES_NOT_EXIST]]></code>
<message><![CDATA[Paper not found.]]></message>
</result>